How to bake a position map in Blender
To bake a position map you need to create an emissive shader and bake in emit mode.

For the node setup use for the input an Input > Texture Coordinate. You will need to use the generated output of the node, by default the axis in Blender aren't the same as most 3D software so you will need to change the RGB channels. For that connect the Generated output to a Converter > Separate RGB and add a Converter > Combine RGB node, here are the connections:


R > R
G inverted > B
B > G


Then add a Color > Gamma and set it at 2.2 to convert the color in Linear, by default it's in sRGB and doesn't work in other software. Then on the Emissive node.

Here is the result and the complete node setup: